DANGEROUS WATERS: Has all the ingredients for a gripping undersea adventure:Ferocious sharks, friendly dolphins, nefarious criminals, and enough chemistry between a sexy heroine and a bold, but sensitive, NYPD detective to spark romance in the steamy Caribbean.

Back on the boat, they were all ecstatic about what they had just experienced. Terry had never seen Mark so animated. “Did you see the action between that sucker and me?” Mark exclaimed, as he pantomimed jabbing at an invisible shark with an imaginary club. They all laughed, and then broke for lunch on the stern of the boat before their next dive.

While eating, they noticed a commotion in the water about a quarter of a mile off the stern. They looked over to see a large group of sea lions frantically swimming toward the shore of a distant island. Suddenly they saw a large great white explode vertically out of the water, with a sea lion firmly clamped in its jaws. They watched in stunned silence as the shark fell back into the water still holding its prize; there were a few ripples, then nothing. It was over as quickly as that. After a few moments the silence was broken by Stan, who said quietly, “Another of our nicknames for ’em is, White Death.”

The sea lions had sensed that a shark was stalking them from below and most made it to safety before the shark had taken a straggler, by using a classic great white hunting technique: swimming below the chosen prey, using its counter-shading for camouflage, then, at the appropriate moment, when escape was impossible, shoot up vertically and capture the unfortunate victim in its jaws, immediately killing or incapacitating it. No one said anything for a few seconds as they watched a red slick of blood slowly dissipate, because, instinctively, each knew what the others were thinking: that a swimmer or someone paddling on a surf board would have had no chance at all against the violence of that type of attack.

“WOW!” Eric finally said. Mark knew that this hunting behavior was seen in some white shark populations but not others. Why? Was this instinct or a learned behavior? Could white sharks teach hunting techniques to their young? Not likely. Sharks do not have a reputation as doting parents. Did sharks observe and imitate the successful hunting tactics of other sharks? Mark discussed his thoughts with Terry and suggested that they tackle this as a future research project after this trip was completed.

The dive plan for the second dive was for Mark and Stan to reverse roles. Stan would be the “bait” and Mark would cover his back. Eric and Terry would continue to serve at photographers, remaining inside the cage. Terry had no desire to be with sharks outside the safe confines of the cage and Eric was on the team because he was a highly regarded underwater photographer, who had a definite aversion to deliberately putting himself in harm’s way.

This time they had to wait almost thirty minutes for the first shark to appear. Stan moved into position, with Mark covering his flank. Everything went smoothly at first. The shark circled, Stan and Mark rotated accordingly. The shark made a pass and Stan deflected it with the shark club. It came in again . . .wait; that was too soon for it to be in position to return. Then they realized it was not one, but a pair of blue sharks. This was why the second diver was in the water. Mark moved so he was positioned back-to-back with Stan, air tanks clanking against each other. Now they could watch both sharks and visually cover a 360-degree radius.

They fended off the sharks while Terry and Eric documented the action. Now there was a problem. They had already been underwater for over 30 minutes before the sharks had appeared and Mark was running low on air, only 700psi remaining. During a momentary lull in the action he signaled Stan to check his air gauge. He was not much better off, at 900psi. If the sharks didn’t leave soon they would have to break their defensive formation, making them vulnerable, then try to get back into the cage as quickly as possible.